DE102013014427A1 - Drive circuit for air bearing motor - Google Patents

Abstract

The invention relates to a drive circuit for an electric motor with aerodynamic mounting of the motor shaft, wherein the drive circuit comprises at least one storage means for storing electrical energy, through which the electric motor can be fed with electrical energy in case of failure of the supply voltage or DC link voltage to a necessary for air storage Minimum speed of the motor shaft to get at least temporarily.

Description

The invention relates to a drive circuit for an electric motor with aerodynamic bearing of the motor shaft.

Air bearings are bearings in which two mutually moving partners are separated by a thin film of air. As a result, they allow an almost frictionless relative movement.

The air bearing can be used in particular in electric motors, in which the driven motor shaft, d. H. the rotor is supported by an air gap in the motor housing. Air bearings distinguish between static bearings and dynamic bearings. For static bearings, the air gap is created by the introduction of compressed air by external means. Dynamic bearings require no compressed air supply, since the compressed air required in the air gap is generated by proper movement. Here, however, there is the problem that the two mutually moving bearing parts can touch below a characteristic relative speed and thus subject to wear and increased friction.

Air-bearing engines are used, for example, in air conditioning systems, especially air conditioning systems for rail vehicles. The air-bearing motors are coupled to a compressor and drive it. Since the air conditioning system, like other consumers within the rail vehicle, is fed by the supply voltage of the overhead line, this power supply can be temporarily interrupted at certain points of transition. Depending on the interruption duration, this can lead to the speed of the air-bearing motors in air conditioning systems suddenly being reduced to a standstill and insufficient compressed air for the air bearing can be generated. This creates harmful friction within the air bearings and the life of the engine is greatly reduced.

The present invention therefore has as its object to provide a solution that prevents the drop in air pressure and speed within the air bearing motor at a short-term or certain interruption of the supply voltage and consequently reduces the wear of the air bearing.

This object is achieved by a drive circuit according to the features of claim 1. Advantageous embodiments of the drive circuit are the subject of subsequent claims to the main claim.

According to claim 1, a drive circuit for an electric motor with aerodynamic mounting of the motor shaft or rotor shaft is proposed. According to the invention, the drive circuit provides at least one storage means for storing electrical energy. The stored energy of the at least one electrical storage means is now to be used to maintain an emergency operation of the electric motor in case of failure of the actual supply voltage. The electric motor is therefore at least temporarily fed in a power failure on the stored electrical energy of the at least one storage means to maintain a minimum speed of the motor or rotor shaft can. The minimum speed is chosen so that just for a satisfactory air bearing of the motor shaft is taken care of.

In one embodiment of the invention, the drive circuit comprises a DC intermediate circuit for supplying the electric motor with electrical energy. At least one electrical storage device is then part of the intermediate circuit. In case of failure of the intermediate circuit voltage, the at least one electrical storage means takes over the power supply of the electric motor.

The electric motor can be designed as an AC motor and is then fed by means of an inverter from the intermediate circuit voltage. The inverter is used to control the engine speed.

It makes sense for the at least one storage means to be chargeable by the supply voltage or the intermediate circuit voltage during normal operation. With sufficient voltage supply, the at least one storage means is charged up to a certain voltage level. This ensures that, in the event of a later power failure of the supply voltage or the intermediate circuit voltage, sufficient electrical energy is available in the storage means.

Ideally, a control is provided which detects a power failure of the supply voltage or the intermediate circuit voltage and switches in this case to the emergency power supply of the electric motor by the at least one storage means. This can be an active switching operation of a specific component. Alternatively, there is the possibility that the at least one storage means is connected to the electric motor in such a way that energy can be provided automatically from the at least one storage means to the electric motor when the supply voltage is interrupted.

The drive circuit may preferably be designed such that it further stabilizes the intermediate circuit voltage during possibly occurring fluctuations in the supply voltage or intermediate circuit voltage allows. Preferably, the control of the drive circuit can be designed such that it detects a falling below a predefined lower limit of the intermediate circuit voltage. In this case, electrical energy can be automatically provided from the at least one storage means in order to support the voltage supply of the electric motor. As a result, the intermediate circuit voltage can be kept almost constant.

The at least one air-bearing electric motor may have at least one coupling agent on the output side. In this case, it is expedient if the control of the drive circuit has corresponding means for actuating this clutch in order to prevent the engine in an emergency, i. H. in case of failure of the supply voltage or intermediate circuit voltage, to switch load-free. As a result, optimum engine operating conditions are created in order to be able to ensure the longest possible supply of the engine from the storage means in the event of a supply interruption.

The at least one electrical storage means may be a low-voltage storage or alternatively a high-voltage storage. Suitable embodiments of the electrical storage means comprise at least one double-layer capacitor and / or at least one rechargeable chemical battery cell, for example a Li-ion cell.

In a preferred embodiment, a measuring means for detecting the temperature of the at least one storage means may be provided. Optimally, the charging voltage of the at least one storage means can then be determined or limited as a function of the measured temperature. In particular, when using double-layer capacitors, the life of the capacitor cells depends on the ambient duration and the applied voltage. The higher the temperature and the selected charging voltage, the more the life of the cells is shortened. In order to decouple the life of the cells from the ambient temperature, the storage temperature is measured and the level of the charge voltage of the at least one storage means is adjusted taking into account the measured temperature.

Ideally, the cell voltages are reduced by about 0.1 V per 10 ° C increase in temperature. In this way, the influence of temperature on the cell life is significantly compensated. However, the invention should not be limited to the exemplified values given.

If a low-voltage storage device is used as storage means, then this can be connected to the supply voltage or the intermediate circuit via a bidirectional DC / DC converter. For the charging of the memory by the intermediate circuit voltage or supply voltage, the DC / DC converter operates in the step-down mode. If the supply voltage fails, the DC / DC converter can be switched to boost mode. The air bearing engine is then supplied from the low-voltage storage. In this embodiment, the DC / DC converter must be galvanically isolated between the low-voltage storage and the high-voltage intermediate circuit.

In a simpler embodiment, the at least one storage means is designed as a high-voltage storage. In this case, a galvanic isolation of the bidirectional DC / DC converter between the intermediate circuit and the storage means is not necessary, which leads to a considerable simplification of the complexity of the overall system.

In a further advantageous embodiment of the invention, the at least one storage means is a high-voltage storage and connected via a unidirectional DC / DC converter to the supply voltage or to the intermediate circuit. The DC / DC converter serves to charge the at least one storage means with the supply voltage or the intermediate circuit. In this case, the DC / DC converter preferably operates in the step-down mode.

Furthermore, the electrical storage can be connected via a diode to the air bearing motor. In case of failure of the supply voltage or the intermediate circuit voltage, the motor is automatically fed via the diode from the at least one storage means with electrical energy.

Alternatively, it is possible to dispense with the use of a DC / DC converter. Instead of the unidirectional DC / DC converter, a resistance element is then used, via which the at least one memory is connected to the supply voltage or the intermediate circuit. The charging current from the DC link can be limited via the resistor element. It is possible to pre-set the resistance value in advance or to use a variable resistance element with adjustable resistance value.

The charging of the storage means via the resistor element, while in case of failure of the supply voltage or the intermediate circuit voltage of the electric motor is fed via a diode from the memory. It makes sense that the resistance element is designed as a switched resistance element, so that the charging process can be stopped if necessary, preferably when the storage voltage of the storage means has reached a predefined voltage level.

The intended control is used to control the DC / DC converter or to control the resistance element. Optionally, the controller takes over the switching of the bidirectional converters between step-up or step-down mode.

Furthermore, it is expedient if the at least one storage means can be monitored by the controller and its storage voltage can be detected. Depending on the measured memory voltage, the controller can actuate the DC / DC converter or the switchable resistor element in order to control or interrupt the charging process as a function of the storage voltage.

Furthermore, the controller is adapted to control or regulate the engine speed via an upstream of the electric motor inverter. The control or regulation is consequently connected to a corresponding sensor system for detecting the engine speed.

According to a further advantageous embodiment of the invention, the inverter can also be supplied with energy at least a short time by the at least one storage means at an interruption of the supply voltage / DC link voltage. The converter requires, for example, electrical energy for operating the driver circuit or sensor system. Preferred is an embodiment of the drive circuit, in which a DC / DC converter of small power is connected in parallel to the at least one memory means to provide the required supply voltage for the inverter during the interruption of the supply voltage / DC link voltage from the at least one storage means and autonomous operation to secure the drive circuit.

In addition to the drive circuit, the invention relates to an air conditioner with an air-bearing motor for driving a compressor and a drive circuit according to the present invention or an advantageous embodiment of the drive circuit. Consequently, the air conditioning system is characterized by the same advantages and properties as the drive circuit according to the invention. A repetitive description is therefore omitted.

The electric motor is preferably connected to the compressor via a coupling means, which switches the electric motor load-free when the supply voltage is interrupted.

The air conditioning is used in particular for use in rail vehicles, wherein the supply voltage is preferably provided by a catenary.

Further advantages and features of the invention will be explained below with reference to several embodiments shown in the drawings. Show it:

1 FIG. 4 is a circuit diagram of a drive circuit for controlling an air bearing engine according to a first embodiment of the present invention; FIG.

2 the drive circuit according to the invention according to a second embodiment,

3 the drive circuit according to the invention according to a third embodiment,

4 : the drive circuit according to the invention according to a fourth embodiment and

5 : the drive circuit according to the invention 4 with an extension to supply the inverter.

All five schematics of the 1 to 5 show a drive circuit with a DC link 10 for the power supply of the electric motor 20 , The motor 20 is an electric motor with aerodynamic bearing of the motor shaft, which serves to drive an air conditioning compressor and is connected thereto via a coupling, not shown.

At the electric motor 20 it is an AC motor. The engine 20 is therefore the inverter 30 upstream, the DC voltage U _ZK of the DC _link 10 converted into the required AC voltage to the motor supply. In addition, the frequency of the generated AC voltage for speed control of the motor 20 adjustable. The desired control of the inverter 30 done by the controller 40 the drive circuit. The controlled variable is the rotational speed ω of the motor measured at the motor shaft and to the controller 40 is transmitted. The control adjusts depending on the setpoint speed 40 then the necessary frequency of the inverter 30 one.

The shown switching structure with an air-bearing motor 20 to drive a compressor is often used in air conditioning systems for rail vehicles. The air conditioning as well as other consumers are powered by the overhead line within the rail vehicle. The power supply can therefore be temporarily interrupted at transition points and fail. Because the engine 20 has an aerodynamic bearing, the effect of the air bearing depends on the speed of the engine 20 from. If the speed falls below a critical limit, it comes into contact between the bearing counterparts and there are unwanted friction within the air bearing, whereby the service life is significantly reduced.

For this reason, according to the invention, an electrical memory 50 . 51 in the DC voltage intermediate circuit 10 integrated, so that the energy required during a power failure of the intermediate circuit voltage U _ZK for the trouble-free operation of the air bearing motor 20 can be made available. The electrical energy of the storage medium 50 . 51 ensures a minimum speed of the motor 20 to just maintain the air pressure inside the air bearing.

During the normal state, the air bearing motor is powered by the power supply system and at the same time the memory becomes 50 . 51 loaded to the intermediate _circuit voltage U _ZK . If the intermediate circuit _voltage U _{ZK is} interrupted for a short time, for example at transition points of the overhead line, the controller recognizes 40 the power failure and provides the power to the motor 20 on the memory 50 . 51 around. At the same time the air bearing engine 20 decoupled from the load. This is done by the output side not shown coupling between the engine 20 and compressor. This will provide optimal operating conditions for the air bearing engine 20 created to a maximum service life of the engine 20 from the storage means and thus to ensure the longest possible maintenance of the minimum speed.

The electric storage 50 . 51 may include a variety of double layer capacitors or rechargeable battery cells, such as Li-ion cells.

For the integration of the memory 50 . 51 in the DC link 10 offer different embodiments, which will be described below with reference to the 1 to 4 be explained in more detail. First, however, a general definition for the dimensioning of the memory 50 . 51 are given. It is assumed that the minimum energy consumption of the engine 20 during the interruption time T equals E, where the formula E = P · T and P is the minimum power required to allow the air bearing motor to be in a safe safe operating mode. The required storage capacity C is then calculated as follows: E = P · T = 1 / 2C (U 2 / SP - U 2 / min)

It follows:

Where U _{Sp is} the voltage of the memory and U _{min is the} minimum required intermediate circuit voltage for safe motor operation.

1 now shows the block diagram of the emergency operable drive system, wherein the storage means as a low-voltage storage 51 is executed. The integration of the storage means 51 in the DC link 10 via the bidirectional DC / DC converter 60 , which also has a galvanic isolation between the intermediate circuit voltage U _ZK and the low-voltage storage 51 creates.

If the power supply system is normal, this will be done by the controller 40 detected and the motor is powered by the power supply, ie the intermediate circuit voltage U _ZK via the inverter 30 fed. At the same time the Niedervoltspeicher 51 through the DC / DC converter 60 charged, this works as a buck converter and the intermediate circuit voltage U _ZK with higher voltage in a lower DC voltage for the low-voltage storage 51 transformed.

In case of failure of the power supply or the intermediate circuit voltage U _ZK is the controller 40 the DC / DC converter 60 in the boost mode, reducing the low voltage of the memory 51 is transformed and the engine 20 over the inverter 30 supplied with electrical energy to maintain the minimum speed. The necessary intermediate circuit voltage is here through the memory 51 provided.

2 shows one opposite the 1 modified embodiment in which instead of a low-voltage memory 51 now a high-voltage storage 50 Use finds. By using the high-voltage memory 50 simplifies the switching structure, in particular the integration of the memory 50 in the DC link 10 , Due to the lower voltage difference, the bidirectional DC / DC converter must 61 no galvanic isolation between the intermediate circuit voltage U _ZK and the voltage level of the high-voltage storage 50 to ensure.

In the embodiment of 3 is also analogous to 2 a high-voltage storage 50 used as storage means. The DC / DC converter 62 works now only unidirectional in the buck converter mode. As a result, the intermediate circuit voltage U _ZK to the required voltage of the high-voltage memory 50 set. In the embodiment shown, the memory becomes 50 thus charged during normal operation by the intermediate circuit voltage U _ZK until a predefined voltage level is reached. After reaching this voltage level, the controller switches 40 the DC / DC converter 62 from.

When the intermediate circuit voltage U _{ZK fails} , the charging process is stopped and the air bearing motor is stopped 20 automatically via the with the DC link 10 connected in the flow direction diode 70 through the store 50 fed.

In the embodiment of 4 is now completely dispensed with the use of a DC / DC converter. Instead, the high-voltage memory 50 in normal operation via a resistor 80 charged by the _DC link voltage U _ZK . The resistance 80 is a switch 90 upstream to the charging process upon reaching a predefined storage voltage of the high-voltage memory 50 to be able to interrupt. The control 40 monitors the memory voltage U _S and optionally opens the switch 90 as soon as the desired voltage is reached. The charging process is then interrupted.

When Au the intermediate circuit voltage U _ZK supplies the high-voltage storage 50 automatically via the flow direction with the DC link 10 switched diode 70 the engine 20 with electrical energy.

wobei U_ZK die Zwischenkreisspannung und I_{Sp_Max} der maximal zulässige Ladestrom des Speichers 50 ist.The resistance 80 limits the charging current during the charging phase, especially when the accumulator is completely discharged. The resistance R of the resistor 80 is calculated as follows:

where U _{ZK is} the intermediate _{circuit voltage} and I _{Sp_Max is} the maximum permissible charging current of the memory 50 is.

The embodiment according to 5 basically corresponds to the design according to 4 , In addition, the DC / DC converter 95 low power in parallel to the high-voltage storage 50 switched to the inverter 30 provide necessary supply voltage for operating the internal driver circuit and sensors during an interruption of the DC link voltage and to ensure autonomous operation of the drive circuit.

Claims (17)

Drive circuit for an electric motor with aerodynamic mounting of the motor shaft, characterized in that the drive circuit comprises at least one storage means for storing electrical energy by which the electric motor can be fed with electrical energy in case of failure of the supply voltage or DC link voltage to a minimum speed required for the air bearing the motor shaft to get at least temporarily. Drive circuit according to claim 1, characterized in that the at least one storage means by the supply voltage or DC link voltage is rechargeable. Drive circuit according to claim 2, characterized in that means for measuring the temperature of the at least one storage means are provided and the charging voltage of the at least one storage means in dependence on the measured temperature is selectable. Drive circuit according to one of the preceding claims, characterized in that a controller is provided which detects a power failure and switches to the emergency power supply of the electric motor by the at least one storage means. Drive circuit according to one of the preceding claims, characterized in that a controller is provided which detects a drop below the supply voltage / DC link voltage of a minimum voltage and the at least one storage means switches on to keep the DC link voltage constant above the minimum value. Drive circuit according to one of the preceding claims, characterized in that the controller is actuated in case of power failure, a driven-side clutch of the electric motor to switch the engine load. Drive circuit according to one of the preceding claims, characterized in that the at least one electrical storage means comprises a low-voltage storage or a high-voltage storage. Drive circuit according to one of the preceding claims, characterized in that the at least one electrical storage means comprises at least one double-layer capacitor and / or at least one rechargeable chemical battery cell, in particular a Li-ion cell. Drive circuit according to one of the preceding claims, characterized in that the at least one storage means comprises a low-voltage storage and is connected via a bidirectional galvanically isolated DC / DC converter with the supply voltage or the intermediate circuit. Drive circuit according to one of the preceding claims, characterized in that the at least one memory means comprises a high-voltage memory and is connected to the supply voltage or the intermediate circuit via a bidirectional non-galvanically separated DC / DC converter. Drive circuit according to one of the preceding claims, characterized in that the at least one storage means comprises a high-voltage storage and is connected via a unidirectional DC / DC converter with the supply voltage or the intermediate circuit for charging the storage means and in case of failure of the supply voltage / DC link voltage of the memory via a diode feeds the electric motor. Drive circuit according to one of the preceding claims, characterized in that the at least one storage means comprises a high-voltage storage and is connected via a resistance element, in particular a switched resistance element, with the supply voltage or the intermediate circuit for charging the storage means and in case of failure of the supply voltage / DC link voltage of the memory via a diode feeds the electric motor. Drive circuit according to one of the preceding claims, characterized in that the state of charge of the at least one storage means can be monitored by the controller and the DC / DC converter or the switchable resistance element in dependence of the state of charge is controlled by the control unit. Drive circuit according to one of the preceding claims, characterized in that the electric motor is powered by a converter by the supply voltage / DC link voltage and the inverter is preferably controlled or regulated by the controller in dependence on the detected engine speed. Drive circuit according to claim 14, characterized in that the converter is connected to the at least one storage means or connectable, in particular via a DC / DC converter to ensure an emergency power supply of the inverter in case of failure of the supply voltage / DC link voltage. Air conditioning system, in particular for a rail vehicle, with an air-bearing electric motor for driving a compressor and a drive circuit according to one of the preceding claims. Air conditioning system according to claim 16, characterized in that the electric motor is connected via at least one coupling means to the compressor and on the output side of the compressor is decoupled in case of failure of the supply voltage / DC link voltage.

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